Classifying apparatus



Feb; 20, 1962 K. R. POWELL CLASSIFYING APPARATUS Filed May 29. 1958 FIG.

INVENTOR.

KEITH R. POWELL BY WJZQ; a M

ATTORNEY United States 3,021,952 Patented Feb. 20, 1962 3,021,952CLASSIFYING APPARATUS Keith R. Powell, Minneapolis, Minn, assignor toGeneral Mills, Inc., a corporation of Delaware Filed May 29, 1958, Ser.No. 738,872 9 Claims. (Cl.'209-339) "by suitable reciprocation rvibration of the sifting unit.

Problems have been encountered in such sifters, particularly those inwhich the sifting surface is enclosed in an outer box or frame, andparticularly when the sifter is subjected to rapid vibratoryreciprocation to convey the stock across the sifting surface. One ofthese problems is that of irregularity, or surging, in the sifting andconveying action of the stock on the surface. It is believed that suchsurging may be due to variations in the instantaneous pressuredifferentials above and below the sifting surface caused by rapidvibrations of the enclosure in'which the sifting surface is mounted.

With these problems of the prior art in view, it is one object of thepresent invention to provide improved classifying apparatus of thereciprocating type. 7

Another object is to provide an improved reciprocating or vibratorysifter having novel means for equalizing or neutralizing pressuredifferentials above and below the sifting surface.

Other objects and advantages will be apparent from the followingspecification, in which certain preferred embodiments of the inventionare described. In general, the above objectives are accomplishedaccording to the present invention by the use of suitable partitions,which are at least partially flexible, at appropriate locations in thesifter body. Such flexible partitions are particularly useful in sealingthe upper chamber above the sifting surface and can be used either atthe inlet or discharge end of the sifter, and are particularly useful atthe inlet end.

In the drawings forming a part of this application:

FIGURE 1 is a side view, partly in section, of a vibratory reciprocatingsifter embodying features of the present invention;

FIG. 2 is a sectional view on the line 22 of FIG. 1;

FIG. 3 is a partial perspective view, with certain portions cut away forclarity, to show the details of one form of flexible partition as usedin FIG. 1; and

FIG. 4 is a partial perspective view of a modified form of partiallyflexible partition.

As shown in FIG. 1, the invention is disclosed in connection with areciprocating vibratory sifter designated generally at 10. Thisclassifying unit includes a body portion having a bottom Wall 12, a topwall 14, side walls 16, and end walls 18 -and 20. The stock to be siftedis shownat 22 and is introduced through a suitable inlet 24 at one endof the sifter near end wall 18; The stock is received on a conveyingsurface 26 which carries the stock along to a sifting or classifyingscreen 28. The stock is adapted to be fed across this screen 28 whiledesired particles are sifted through the surface 28 to the bottom 12 ofthe housing. The particles thus sifted are discharged through an outlet36, while the particles which do not pass downwardly through the siftingsurface 28 are carried over the tail surface 32 and discharged throughan outlet 34 adjacent end wall 20.

The sifter is supported for suitable vibratory reciprocation on hangers36 having their lower ends 38 pivoted to the sifter body and their upperends 49 pivoted to a suitable frame member 42. The hangers may beinclined as shown in FIG. 1 to provide both an upward lifting and ahorizontal conveying movement to the stock as shown by the two-headedarrow 43, which extends perpendicularly to the intermediate or restposition of the hangers 36.

The desired vibrations of the sifting unit are provided through a driveshaft 44 having one end secured at 46 to the sifter body and having itsother end driven by a suitable eccentric 48-or other vibratory powersources. This eccentric, in turn, is driven by a suitable motor and gearbox indicated generally at 50 and the frequency of vibration may becontrolled by a suitable speed control handle 52.

The stock 22 is fed into the inlet 24 through a flexible connection 54from a supply spout 56. Similar flexible connections 62 and 64 connectthe discharge spouts 30 and 34 to appropriate subsequent apparatus; thusthespout 30 is connected to a further conveying tube 66 which feeds thematerial to a receiving hopper or other processing unit 68, while theoutlet 34 is connected by its sleeve 64 to a suitable further processingunit or hop per 70.

As described up to this point, the sifter 10 is essentiallyconventional. It has been observed, however, in connec' tion with suchsifters, that the stock 22 does not always feed evenly along the siftingsurface 28 and may, in fact, bunch up or collect at certain portions ofthe surface, while leaving other portions of thesurface essentiallybare. The present invention is based on the belief that thesedifliculties in feeding and sifting of material may be due to thefailure of prior Workers to recognize that an enclosed vibratory sifterof this type inherently creates variable instantaneous pressuredifferentials above and below the screen. Thus, when the sifter is movedto the right in FIG. 1, the closed inlet end 18 of the sifter body tendsto push the column of air below sifting surface 28 toward the right tocause an increase in pressure along this 'air column or slug of air. Theincrease in dynamic pressure at various points beneath the siftingsurface 28 appears to depend on the total length of the air columninvolved bet-ween walls 18 and 20 and on the relative distancefrom endwall 18. Above the siftingsurface 28, there is less tendency to generatedynamic pressures in the longitudinal column of air because the inletopening 24 may dissipate some of the pressures generated by end wall 18above the screen. Thus, an instantaneous pressure differential may becreated as the sifter is moved upwardly and to the right and thispressure differential, particularly near the inlet end, may lift thestock upwardly from the surface 28 just at the point when it should bein contact withsuch surface to obtain the desired conveying'movement.Conditions may be reversed on the return stroke, when movement of endwall 18 to the leftin FIG. 1 may tend to pull the respective air columnsto the left and create instantaneous decreases in dynamic pressure.Similar phenomena are believed to occur at the discharge end of the,sifter with respect to end wall 20 and the various wall portions of thedischarge outlets 30 and 34.

According to one feature of the present invention an effort is made toequalize the pressure variations in the air slugs or columns above andbelow the sifting surface by the introduction of suitable flexiblepartitions at appro' priate points in the sifter body. In connectionwith the inlet of the sifter, it has been found particularly helpful tointroduce a flexible partition 72 above the initial receiving surface 26which receives the stock 22. This partition 72 may be made of rubber,plastic, cloth, or other relatively flexible material, having its upperportion secured to a suitable cross member 74 secured to thetop I wall14 of the sifter body. This upper portion 76 of the flexible partitionhangs generally vertically from its support 74.

The total vertical length of the flexible partition is somewhat greaterthan the vertical spacing between the top wall 14 and the surface 26.Thus the lower end of the flexible partition at 78 is inclined away fromthe inlet toward the outlet end of the sifter, as shown in FIG. 1,

' to permit the stock 22 to pass beneath this partition. The

flexibility of the partition, and its owninherent weight, tend to holdthe trailing end 78 of the partition in contact with the stock and thusseal oft the inlet end of the air column above sifting surface 28 andeffectively isolate it from the inlet opening 2 4.

In operation the partition 72 serves in a manner similar to end wall 18and is believed to generate dynamic pressures above the sifting surfacewhich are in phase with reciprocation of the sifter and which caneffectively equalize or neutralize the pressures generated below thatsurface by end wall 18. Thus the contact of the stock 22 with siftingsurface 28 and the action of that surface on the stock will beessentially the result of the desired vibration of the sifting surfaceand will not be substantially affected by undesired air pressures anddifferential pressures generated by the reciprocating movement.

According to a further feature of the invention it is possible toutilize a similar flexible partition 80 supported on a cross member 82near the discharge end of the sifter and above the sifting surface 28.In some cases it may be desirable to utilize a similar flexiblepartition 84 beneath the sifting surface 28 and between the end of thatsurface and the discharge outlet 30. Such a partition may be mounted ona cross member 86 to provide essentially identical end wall conditionsat the discharge ends of the respective longitudinal air columns aboveand below the sifting surface 28.

FIG. 4 shows a modified form of partially flexible partition for useaccording to the present invention. Here the partition 88 includes arelatively rigid upper portion 90, which may be secured to a suitablecross member 92 in the sifter body by bolts 94. This portion 90 providesa solid wall portion throughout a. major part of the cross sectionbetween the sifting surface and top of the sifter. The lower portion ofpartition 88 is made of flexible material 96, secured at 98 to theportion 90.

Just as in the case of the completely flexible partition of FIGS. 1 to3, the flexible portion 96 of partition 88 in FIG. 4 will tend toaccommodate itself to the surface of the stock received by the sifter.These flexible portions will thus maintain a suitable air sealregardless of variations in the rate of feed of the stock beneath thepartition. At the same time the angular orientation of these flexibleportions toward the discharge end of the sifter will permit them toincrease or decrease their spacing above the sifting surface inaccordance with the rate of stock feed.

According to the. foregoing description, this invention contemplates theuse of at least partially flexible partitions at appropriate locationsto equalize the variations in dynamic pressures above and below asifting surface in a vibratory sifting unit. While these partitions haveparticular utility in connection with vibratory reciprocating sifters ofthe type shown in FIG. 1, they are believed to have applicatiton tocertain other types of sifters in which similar surging problems may beencountered. The foregoing specification includes a description of theprinciples which are believed to be involved in the present invention,together with some of the ways in which the" invention may be practiced.

Now, therefore, I claim: 1. In a vibratory classifying unit comprising asifting surface having receiving and discharge ends, a body portionhaving top, bottom, side and end walls enclosing said sifting surfaceand providing substantially closed upper and lower chambers aboveandbelow said surface, means for reciprocating said body chambers andsifting surface as a unit longitudinally along a desired path andthereby conveying stock from said receiving end to said discharge endwhile classifying the stock by said surface, an inlet for stock at oneend of said upper chamber, and an outlet for stock at the other end ofeach chamber, the improvement comprising an anti-surging partitionlocated .in said upper chamber between said inlet and the receiving endof the sifting surface at a point adapted to provide desired dynamic airpressures above said sifting surface, said partition having its upperedge secured in air tight relation adjacent said top Wall and its upperportion extending downwardly across the entire width of the upperchamber toward said sifting surface and secured for longitudinalreciprocation with said body and sifting surface, at least the lowerportion of said partition consisting of flexible, airtight materialextending toward said outlet and located to engage the top of the stockon said sifting surface and maintain a substantial air seal between themain portion of said upper chamber and said inlet.

2 A classifying unit according to claim 1 in which both the upper andlower portions of said partition consist of flexible material.

3. A classifying uni-t according to claim 1 in which said partitioncomprises a rigid, substantially vertical upper portion extendingdownwardly from said top wall to a level spaced above the siftingsurface and a lower portion of flexible material extending downwardlytoward said surface and longitudinally toward said outlet.

4. A classifying unit according to claim 1 having a second partition ofsimilar construction located adjacent the outlet from said upper chamberand thereby providing a sealing wall between said upper chamber andoutlet.

5. A classifying unit according to claim 4 having a third partition ofsimilar construction located adjacent the outlet from said lower chamberand thereby providing a sealing wall between said lower chamber andoutlet.

6. A reciprocatory classifying device comprising a sifting chamberenclosed by a plurality of wall members, means for reciprocating saiddevice including said chamber and wall members along a given path, inletmeans in said chamber for feeding stock to be classified thereto, outletmeans for discharging the classified stock, a sifting surfaceintermediate said inlet and outlet means for classifying said stockduring said reciprocation, a substantially imperfo-rate receiving plateat one end of said sifting surface below said inlet means, a relativelyairtight discharge plate at the opposite end of said sifting surfaceadjacent said discharge means and flexible anti-surging partition meansdisposed above at least one of said plates and reciprocable with saidchamber, said partition having a substantial area transversely of saidpath located and arranged to move the volume of air withinsaid chamberin phased relation to the reciprocation of said chamber and therebyprovide improved sifting and conveying.

7. An improved classifying device, the combination comprising arectangular sifting chamber enclosed by a plurality of Wall members, andprovided with a classifying surface therein, inlet means for admittingstock to said classifying surface, means for moving said chamber andsaid classifying surface as a unit relative to said stock along adesired path, said stock being classified by said movement, outlet meansin said chamber for discharging the classified stock, and flexibleanti-surging partition means located between said classifying surfaceand said outlet means and extending substantially normal to said pathand movablewith said chamber and surface thereby moving a'volume of airwithin said chamber in correlation to the movement of said classifyingsurface.

8. An improved classifying device, the combination comprising arectangular sifting chamber enclosed by a plurality of wall, members,and provided with a subt nti lly horizontal classifying surface therein,inlet means for admitting stock to said classifying surface, means formoving said chamber and said classifying surface as a unit relative tosaid stock along a desired path, said stock being classified by saidmovement, outlet means in said chamber for discharging the classifiedstock, and flexible partition means located adjacent each of said inletand outlet means and extending transversely of said path, said partitionmeans moving with said chamber and moving air within the chamber therebygenerating dynamic aid pressures ofi setting undesired pressuredifferentials resulting from movement of the volume of air within saidchamber.

9. The device of claim 8 wherein each flexible partition means ispositioned generally perpendicular to the direction of flow of the stockand has at least one yieldable longitudinal edge in engagement with saidstock and References Cited in the file of this patent UNITED STATESPATENTS 398,692 Bittinger Feb. 26, 1889 418,587 Prinz Dec. 31, 1889 1,214,506 Brasack Feb. 6, 1917 1,629,244 WillcoX May 17, 1927 1,686,107Sewell Oct. 2, 1928 2,047,713 Simpson July 14, 1936 2,903,135 Dryg Sept.8, 1959 FOREIGN PATENTS 7 3,646 Germany Apr. 5, 1893

